The subject matter of the present invention is a method and device for the near-surface, non-destructive inspection by means of ultrasound of a rotationally symmetric workpiece having a diameter that changes from section to section. In this case, the workpiece does not have an internal cut-out. The method and the device are suited, in particular, for the inspection of a workpiece with an anisotropic sound velocity. For example, an anisotropic sound velocity is frequently observed, for example, in forged solid shafts which can be used, for instance, in rail vehicles.
Wheel sets of rail vehicles generally include one pair of wheels mounted on a rigid solid or hollow shaft. The shafts used in this case often have external diameters changing from section to section, for example defined regions for the accommodation of functional components, such as the wheels, anti-friction bearings or brake disks. It is obvious that the shafts of wheel sets of rail vehicles constitute safety-relevant components that are subject to natural wear over the long life span of rail vehicles. For this reason, their freedom from flaws has to be determined by means of non-destructive inspection methods not only during the production of wheel sets for rail vehicle. Rather, a regular inspection with regard to freedom from flaws of all components, in this case particularly the wheels as well as the shaft used, is required also over the entire life span of a wheel set. In practices, the most frequent wear phenomenon observed in shafts of wheel sets of rail vehicles is the occurrence of incipient cracks, i.e. crack-like fatigue failures that start at the surface of the respective shaft. Every rail vehicle operator there-fore has to provide suitable inspection methods and devices in order to check the wheel sets of rail vehicles with regard to their freedom from flaws regularly.
Until this day, the inspection by means of ultrasound of rotationally symmetric workpieces having diameters that change from section to section, in particular of solid shafts of rail vehicles, constitutes a particularly challenging inspection task. On the one hand, this is due to the fact that, as a rule, rotationally symmetric workpieces with a diameter that changes from section to section only have few surfaces suitable for coupling in ultrasound. Furthermore, such workpieces are often forgings. As a rule, they have an increased anisotropy of the sound velocity for ultrasound.
Moreover, the inspection of a wheel set of a rail vehicle often entails a downtime 5 of the rail vehicle, which is directly connected to high downtime costs due to the rail vehicle being out of service. In order to minimize them, it would be desirable to be able to inspect a fully assembled wheel set, i.e. a wheel set with assembled bearings and/or brake disks. If they are mounted, then an insonification from the shaft or from the end face (e.g. by means of a conical probe) is not possible with the inspection methods known from the prior art.
Finally, the generation of an easily interpreted representation of the results of an ultrasound inspection obtained on a rotationally symmetric workpiece constitutes a problem which, as far as the applicant is aware, is so far unsolved.